I propose to continue my work on the genetic control of mutation. The emphasis will be on Escherichia coli mutator genes, a mutator gene being defined as a mutant gene that increases rates of mutation throughout the genome. The relationship between the ultraviolet-light sensitive mutation mutation uvrE and the very closely linked uvrD mutation will be studied. Mutator mutations will be induced by the insertion of transposable drug resistance elements. These will be useful in genetic manipulation and will be used to find suppressors of mutator mutations. The relationship between increased recombination and the mutator mutations will be examined. A possible effect of mut mutations on the rate of joining of nascent DNA fragments in polA strains will be studied. Genetic or recombinant DNA techniques will be used to construct mut phages. Such phages will allow the identification of mutator gene proteins. It is hoped that this work will give increased understanding of the role of mutator gene products and their involvement in the accuracy of DNA replication.